1. Field of the Invention
The present invention relates to a honeycomb filter.
2. Discussion of the Background
In recent years, it has become a serious issue that particulate matter (hereinafter, referred to simply as particulate) contained in an exhaust gas discharged from internal combustion engines of vehicles such as buses and trucks and construction machines causes harmful effects on the environment and human being.
Therefore, various kinds of honeycomb filters made of porous ceramics have been proposed as a filter for capturing the particulate contained in an exhaust gas and thereby purifying the exhaust gas.
FIG. 3 is a perspective view schematically showing one example of a conventional honeycomb filter of this kind, FIG. 4(a) is a perspective view schematically showing a honeycomb fired body constituting the honeycomb filter, and FIG. 4(b) is a cross-sectional view along the line A-A of FIG. 4(a).
In the honeycomb filter of this kind, as exemplified by a conventional honeycomb filter 70 shown in FIG. 3, a plurality of honeycomb fired bodies 80 comprising silicon carbide and the like are bonded to each other by interposing an adhesive material layer 72 to compose a ceramic block 71, and a coat layer 73 is formed around the ceramic block 71.
In each of the conventional honeycomb fired bodies 80, as shown in FIGS. 4(a) and 4(b), a large number of cells 81 are longitudinally placed in parallel with one another and cell walls 83 partitioning the cells 81 from one another work as a filter. In other words, each of the cells 81 formed in the honeycomb fired bodies 80 is sealed with plugs 82 in one of the end parts in an inlet side or an outlet side of the exhaust gas as shown in FIG. 4(b) so that the exhaust gas introduced into one cell 81 is flow out of another cell 81 after surely passing through the cell wall 83 partitioning the cells 81.
In an exhaust gas purifying apparatus, the honeycomb filter 70 with the above-mentioned configuration is installed in an exhaust path of the internal combustion engine, and the particulate contained in the exhaust gas discharged from the internal combustion engine is captured by the cell wall 83 while passing through the honeycomb filter 70 so that the exhaust gas is purified.
As an example of a honeycomb filter, WO 2003/002231 A1 discloses a honeycomb filter formed by integrating a plurality of honeycomb segments with a honeycomb structure having a large number of communication holes, in which a heat capacity per unit volume of the honeycomb segment in the outer peripheral part is higher than that of the honeycomb segment in the center part. The contents of WO 2003/002231 A1 are incorporated herein by reference in their entirety.